Lyophilizer

Most recent answer: 10/22/2007

Q:
I’ve been studying the phase diagram for water and haven’t been able to figure out why water remains frozen under a vacuum (<500mT) at room temperature in a lyophilizer. Samples are initially frozen prior to placing on the lyophilizer.
- Greg (age 13)
SPHS, CA
A:
The water won’t stay frozen forever. It gradually sublimes (turns from a solid into gas). If I remember my lyophilizers right from days in a botany lab, the water doesn’t really reach room temperature. It takes heat (roughly the sum of the latent heats of the solid/gas and gas/liquid transitions) to convert those water molecules to vapor. That keeps the remaining water cold. That’s the same effect that cools your skin when water evaporates from it, only more so. So I believe the water remains frozen because it remains cold.

Mike W.

(published on 10/22/2007)